The present invention relates to a powdery material for the preparation of a drug-coating solution which is used for coating the surface of, for instance, medicinal tablets in order to suppress the bitterness thereof.
The surfaces of medicinal tablets having a bitter taste are frequently coated with a water-soluble film for the purpose of making the administration thereof easy. Hydroxypropylmethyl cellulose has most widely been used as a material for such film coating. In addition, methyl cellulose has likewise been used.
A coating solution obtained by dissolving a powdery material as a starting material is used for coating tablets with films. In the early 1950s when the technique for coating the surface of medicinal tablets was developed, a coating solution was prepared by dissolving starting particles for film-coating in an organic solvent. For instance, the material for film-coating was once dispersed in a poor solvent and then the resulting dispersion was mixed with a good solvent to give a coating solution. This method permitted the preparation of a uniform solution within a short period of time. Water has been used instead of organic solvents for reducing the cost required for coating and for the requirement of environmental protection since the early 1970s. However, the use of water as a solvent requires time-consuming and complicated operations such as heating and cooling operations in the preparation of a coating solution. If a powdery material such as hydroxypropylmethyl cellulose is directly introduced into water being at room temperature, the material forms large agglomerates in water and the dissolution of such agglomerates requires a long time period on the order of several hours to one day. For this reason, particles of, for instance, hydroxypropylmethyl cellulose are, in fact, dispersed in hot water in advance and then the resulting dispersion is cooled to room temperature. However, it takes about several hours to obtain a uniform solution even when the resulting hot solution is cooled with cold water.
Since the improvement of production efficiency can be ensured by substantially reducing the time required for the preparation of a coating solution, there has been adopted a method in which a material for film-coating is introduced into water on the day before the practical use thereof and kept to stand over night. If it is planned to perform a film-coating process after the end of consecutive holidays, the preparation of a coating solution is started before the consecutive holidays and allowed to stand over 2 to 3 days. Any preservative cannot be added to coating solutions since any drug cannot include such a substance and, therefore, the coating solution is putrefied while storing it and cannot be used in the worst case.
Ideally speaking, a coating solution is thus prepared immediately before the practical use in order to prevent any decay of the solution prepared. To prepare a coating solution immediately before the practical use, a homomixer is in general used. However, this practice suffers from various problems. For instance, too much expenses are required, a large amount of foam is formed depending on the conditions for dissolution and it takes, instead, a long time for completely removing the foam.
An agent for promoting dissolution of a starting material may be used to prepare a coating solution ready for use without using any machinery. Some starting materials such as hydroxypropylmethyl cellulose can be commercially available in the form of, for instance, solution type and powder type premixes which are previously admixed with additives such as pigments, plasticizers and surfactants. These additives previously added to these starting materials have the effect of promoting the dissolution of the starting materials and thus the solution type premixes can be used as such or after being diluted with water. Examples of such premixes commercially available include Opadry available from Colorcon Company which is powder type one and has widely been used. A plasticizer such as polyethylene glycol (PEG) having a surface active effect is inevitably incorporated into the premixes of powder type to improve the dispersibility thereof. The powdery premix permits the immediate preparation of a coating solution by the use of water at room temperature as disclosed in Japanese Paten,: Application Publication No. 2-29655. However, these additives may possibly affect the stability of medicinal substances to be coated with the resulting coating solution and may lead to an increase in its cost.
Under such circumstances, there has been desired the development of a powdery starting material for preparing a solution used in coating of medicinal tablets that does not require the use of any particular machinery and the addition of any other additive and that ensures high medical safety and a high dissolving rate.